In many wireless systems Shared Control Channels (SCCHs) are used in the physical layer to carry transport channels in the downlink direction. For example, in UMTS the Physical Downlink Shared Channel (PDSCH) can be used to carry the Downlink Shared Channel (DSCH) transport channel.
Shared Control Channels are used to convey information on which user equipments are scheduled on what resources (including time, frequency and code resources) and how user equipments should decode the transmitted signal. The Shared Control Channels typically address user equipments in active modes (i.e. non-power saving modes). Recently, it has however been proposed to use Shared Control Channels also for addressing user equipments in power saving modes (e.g. in discontinuous reception modes or idle modes). Thereby the need for a dedicated physical channel to support, e.g., the paging transport channel is eliminated. For example, in a Universal Mobile Telecommunications System (UMTS) the Secondary Common Control Physical Channel (S-CCPCH) has the (dedicated) task to carry the Paging Channel (PCH) and the Forward Access Channel (FACH).
In order to achieve frequency and intercell interference diversity (such as to allow the Shared Control Channels to experience an average of the intercell interference and to avoid them being affected by single high power interferers), these physical channels should be interleaved (or ‘spread’) over a wide frequency band. In OFDM-based communication systems such channels should, e.g., be interleaved over a pseudo-random set of subcarriers covering a large part of the total system bandwidth.
On the other hand, in order to limit power consumption in user equipments that are receiving (and/or detecting) the Shared Control Channels, it is desirable to interleave said Shared Control Channels on a frequency band that is as narrow as possible. This is due to the fact that power consumption can be regarded as a function that increases with the receiver bandwidth, i.e. receiving a wide-band signal consumes more power than receiving a narrow-band signal. This is especially important for user equipments in power saving modes because in such modes, in which user equipments normally spend most of their time, the power that need to be spend for reception of the Shared Control Channel constitutes a considerable amount of the overall power consumption and, hence, directly affects the stand-by time of the mobile.